#include <stdio.h>
#define DIM 2000001

char v[DIM];
long n,i,j,w;

  FILE *f = fopen("ciur.in", "r");
  FILE *g = fopen("ciur.out", "w");

int main(){

  fscanf(f,"%ld",&n);

  for (i=2; i<=n; i++)
    if (!v[i]) {
      w++;
      for (j=2*i; j<=n; j+=i)
	v[j] = 1;
    }

  fprintf(g,"%ld",w);

  fclose(f);
  fclose(g);

  return 0;
}